3GPP and 3GPP2 are standards bodies that are considering the long term evolution of wireless communication systems. The bodies have promulgated specifications for feedback in next generation networks.
In particular, wireless specification 3GPP 25.814 provides that, for any additional feedback required for preceding, any related computational complexity that is incurred due to the additional feedback should be taken into account.
Further, the specification states that a codebook based feedback method should select a pre-coding vector from a codebook in order to reduce signaling overhead. The size of the codebook should be minimized and the codebook should be static.
Irrespective of whether a codebook is used, the amount of feedback should be minimized. Furthermore, an update interval of the selected pre-coding vector should be sufficiently short to track instantaneous channel variation. Thus, efficient methods for feedback are desirable for next generation wireless networks, particularly multiple-input/multiple-output (MIMO) systems.